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Found this useful for scripts where I needed to work with the machine's IP. If $DEVICE is not specified, this will return all IPs on the machine. If $DEVICE is set to a network adapter, it will return just that adapter's IP.

The command above has been changed due to very good constructive criticism - thanks x 2! This command can be used after acquiring mac's, ip's and hostname's or any of the above from a freshly scanned LAN. User must be root, and remember to change your settings on your network managing software manually (Fedc10 NetworkManager Applet 0.7.1 is mine) instead of 'auto DHCP'. You can also substitute eth0 for wlan0 etc - be good and ENJOY!

This is useful if you have need to do port forwarding and your router doesn't assign static IPs, you can add it to a script in a cron job that checks if you IP as recently changed or with a trigger script.

On the Mac, the format ifconfig puts out is little different from Linux: the IP address is space separated, instead of colon. That makes parsing the IP address easier. See releated command for Linux/Unix: